Abbreviations as used herein are as follows:
APNAccess Point NameBLERBlock Error RateBM-SCBroadcast Multicast-Service CenterDRBDefault Radio BearereMBMSEvolved Multimedia Broadcast Multicast ServiceeNBEvolved Node B (also called base station, RNC, etc.)EPCEvolved Packet CoreE-RABEUTRAN Radio Access BearersEPSEvolved Packet SystemE-UTRAEvolved Universal Terrestrial Radio AccessE-UTRANEvolved Universal Terrestrial Radio Access NetworkGBRGuaranteed Bit RateGCGroup CommunicationGC-ASGroup Communication-Application ServerGCSEGroup Communication System EnablerIMSIP Multimedia SubsystemLTELong Term EvolutionMACMedia Access ControlMBMSMultimedia Broadcast Multicast ServiceMBMS-GWMBMS-GatewayMBSFNMultimedia Broadcast Multicast Service Single FrequencyNetworkMCEMulti-Cell/Multicast Coordination EntityMCHMulticast ChannelMCCHMulticast Control ChannelMCSModulation and Coding SchemeMMEMobility Management EntityMRBMBMS Point to Multipoint Radio BearerNASNon-Access StratumOMA-DMOpen Mobile Alliance - Device ManagementPDCPPacket Data Convergence ProtocolPDN-GWPacket Data Network GatewayPMCHPhysical Multicast ChannelRNCRadio Network ControllerRRCRadio Resource ControlRSRPReference Signal Received PowerRSRQReference Signal Received QualitySIBSystem Information BlockSINRSignal to Interference Noise RatioTMGITemporary Mobile Group IdentityQCIQoS Class IdentifierQoSQuality of Service
MBMS (Multimedia Broadcast Multicast Service) is a point-to-multipoint service specified by the 3GPP where data can be transmitted from one source to multiple receivers. Evolved MBMS (eMBMS) was defined in 3GPP LTE Releases 10 and 11 to improve the performance using flexible and enhanced bit rates, single frequency network (SFN) operations and physical layer carrier configuration flexibility (see, for reference, D. Lecompte, et al.: “Evolved Multimedia Broadcast/Multicast Service (eMBMS) in LTE-Advanced: Overview and Rel-11 Enhancements”, IEEE Commun. Mag., vol. 50, no. 11, pp. 68-74, November 2012, briefly denoted [1] hereinafter). It also enables delivery of high-quality content to multiple UEs with enhanced QoS in areas which MBMS services are provisioned. A possible deployment option of MBMS service using a pre-defined area is as shown in FIG. 1.
In FIG. 1, MBSFN service area is the area where all eNBs can be synchronized to provide MBSFN transmission and could contain multiple MBSFN areas. As seen in FIG. 1, an (e)MBMS service area can include multiple MBSFN areas, but also single eNBs that are not part of any MBSFN area. From a UE perspective, all transmissions from a single MBSFN area eNBs are seen as a single transmission. The cells within an MBSFN area will advertise its availability and UEs can consider a subset of MBSFN areas that are configured. As shown in the figure, there could be reserved cells within MBSFN area which does not have any MBSFN transmissions and can use the resource allocated for MBSFN in neighboring cells for other services. In other words, these reserved cells transmit the (e)MBMS data in different radio resources than the MBSFN area. But the maximum transmit power that can be allocated for such resources are limited so as to not cause interference to MBSFN cells. MBMS reception is possible for UEs in RRC_CONNECTED or RRC_IDLE states. Whenever receiving MBMS services, a user shall be notified of an incoming call, and can make outgoing calls (as specified in 3GPP TS 36.300, “E-UTRA and E-UTRAN: Overall description; Stage 2,” v 11.5.0, March 2013, briefly denoted [2] hereinafter). As explained, the terms MBSFN service area and (e)MBMS service area have different meaning, but in the context of the present invention these terms may be used in an interchangeable manner, i.e. expressing in general an area where the UE receives (e)MBMS data via (e)MBMS bearer service.
An (e)MBMS bearer service is identified by an IP multicast address, an APN network identifier and also by a TMGI (Temporary Mobile Group Identity) inside one PLMN. With other words, the UE can use the TMGI as ID for the (e)MBMS bearer service over certain access technology. For example the UTRAN MBMS bearer service and the E-UTRAN eMBMS bearer service would have 2 different TMGIs.
The reference architecture of MBMS is as shown in FIG. 2. Here, Multi-Cell/Multicast Coordination Entity (MCE) could be a functional entity which could be either stand-alone node or a part of another network node (e.g. eNB as shown in FIG. 3 (b)). The MCE takes care of admission control, counting results of MBMS services, and resumption or suspension of MBMS sessions depending in the counting results. The M3 reference point is specified for the control plane between MME and E-UTRAN, assuming that the MCE is a part of the E-UTRAN. The details of the (e)MBMS reference points and related functional entities can be found in the above mentioned standard document [2].
Two possible deployment alternatives that are considered in [2] are shown in FIG. 3, with additional consideration of an X2 interface between eNBs for the present invention. Currently, the services which are envisioned to be provisioned using MBMS are streaming of audio and video, updates of smartphone applications, etc. (as outlined in [1]). It is also considered that the regions where these services are to be delivered will be pre-planned and service continuity over the MBSFN area is enabled by using careful prior planning of the network. The service continuity is enabled as the MBMS service data is delivered in the same radio resources in the cells participating in the MBSFN area. In the boundary area of two cells, the UE can combine the signals coming from the two cells, and therefore, the probability of correct reception is increased. The detailed physical layer parameter configurations for the MBMS feature are available in 3GPP TS 36.331, “E-UTRA: RRC Protocol Specification,” v 11.2.0, briefly denoted [3] hereinafter). Some of the key features of Multicast Channel (MCH) defined in [2, 3] are the requirement to be broadcast in the entire coverage area of the cell, support for MBSFN combining of MBMS transmission on multiple cells, and support for semi-static resource allocation e.g. with a time frame of a long cyclic prefix. The mapping of downlink transport and physical channels are as shown in FIG. 4.
Here, the MBMS control information is conveyed using MCCH logical channel and user data using MTCH logical channel which can be used for multiple MBMS services within an MBSFN area. For simplicity we refer to the multicast transmission over the Core network and over the Radio Access Network (RAN) as point-to-multipoint (P2M) bearer. More specifically, the P2M bearer uses the mechanisms specified in 3GPP for transmission of data from BM-SC to UE.
Mobility aspects of UEs moving out from a MBSFN area to other neighboring cells where the MBMS service is broadcasted/multicasted on different radio resources, but still service continuity is expected has not been considered yet. The reason for this is that current MBMS applications are mainly streaming applications and short interruption perceived by the user is not critical. However, for new services, e.g. as currently studied in 3GPP is ongoing related to Group Communication System Enablers for LTE (GCSE_LTE) (see, for reference 3GPP TS 22.468, “Group Communication System Enablers for LTE: (GCSE_LTE) Release 12,” ver 0.3.0), radio resource efficiency via MBMS transmission and service continuity are key features. Key criteria for radio resource efficiency is “to avoid duplicated/unnecessary radio resources allocated for different group members in a certain cell” and “to minimize impact on signaling plane for the network”. If many UEs are located in the same area, then MBMS is considered as one of the potential technologies to achieve this resource efficiency when transmitting Group Communication (GC) service data (see, for reference S2-131509, “Architecture & functional requirements for GCSE_LTE,” Qualcomm Incorporated). In cells where there are only few UEs, the network may decide to distribute the GC service data in unicast way.